How do you mean "bad, buzzy"....too much high end? Try an EQ pedal in the fx loop. Its really just a jazzed up JCM800 front end. Mods here are real shaky ground because we don't know what sound you're going for, what guitar(s) you use, what p-ups, what spkrs, etc. I can't read some of the values on the schem you posted. Is there a larger version?